Fiber-reinforced collagen composition and process for preparing same

ABSTRACT

AQUEOUS SWOLLEN COLLAGEN OF DOUGH--LIKE CONSISTENCY IS RAISED IN PH WHEREUPON IT DE-SWELLS OR SHRINKS. FIBER REINFORCEMENT CAN THEN BE STIRRED INTO THE AQUEOUS PHASE. UPON RE-ACIDFICATION, THE COLLAGEN AGAIN SWELLS WITH THE FIBER RE-INFORCEMENT DISTRIBUTED SUBSTANTIALLY UNIFORMLY THERETHROUGH. IF DESIRED, A DISPERSION OF AN ESTER OF POLYACRYLIC ACID OR POLYVINYLIDENE CHLORIDE CAN BE INCORPORATED IN THE MASS, PREFERABLY BEFORE RE-SWELLING. THE PRODUCT CAN THEN BE SHAPED IN KNOWN MANNER, AS BY EXTRUSION, AND DE-WATERED AS BY COAGULATION AND/OR DRYING.

United States Patent 3,806,350 FIBER-REINFORCED COLLAGEN COMPOSITION ANDPROCESS FOR PREPARING SAME Joachim Kuhn, and Peter Bohm, Hohensachsen,Germany, assignors to Carl Freudenberg, Patentableilung, Weinheim,Germany No Drawing. Continuation-impart of abandoned application Ser.No. 55,557, July 16, 1970. This application Dec. 29, 1971, Ser. No.213,832 Claims priority, application, Germany, July 28, 1969, P 19 38188.5 Int. Cl. C08h 7/00 US. Cl. 106-124 8 Claims ABSTRACT OF THEDISCLOSURE Aqueous swollen collagen of dough-like consistency is raisedin pH whereupon it de-swells or shrinks. Fiber reinforcement can then bestirred into the aqueous phase. Upon re-acidfication, the collagen againswells with the fiber re-inforcement distributed substantially uniformlytherethrough. If desired, a dispersion of an ester of polyacrylic acidor polyvinylidene chloride can be incorporated in the mass, preferablybefore re-swelling. The product can then be shaped in known manner, asby extrusion, and de-watered as by coagulation and/or drying.

This is a continuation-in-part of application Ser. No. 55,557, filedJuly 16, 1970, now abandoned.

The present invention relates to distributing a fiberreinforcementuniformly through collagen.

It is known that animal hides comprise collagen which in turn comprisesskin fibers. 'Ihe fibers in turn comprise smaller units known asfibrils, e.g. as described in British Pat. 991,183 and in the article,Ultrastructure of Protein Fibers in the publication Collagen, AcademicPress, New York (1963), pp. 19 to 37. The assumption stated in BritishPat. 991,183 that the fibrils are surrounded by an elastic membrane andthat a fiber is the sum of all of the fibrils held together by themembrane is no longer sustained today, but it is generally recognizedthat a collagen skin is constructed of skin fibers and fibrils.

In addition to the tanning of natural hides in the manufacture ofleather, collagen is also involved in the manufacture of syntheticsausage casings. For this purpose the hide is first soaked andmechanically ground so that the fibers are separated from one another.This also results in a destruction of the fibers, to some extent, withthe release of the fibrils. The softened mass of hide fibers is thenextruded through annular slits in the form of tubing. Such tubing hasbeen used for decades as synthetic sausage casings under the designationNaturin. The manufacturing processes entailed are disclosed in GermanPats. 650,526, 650,887, 659,490, 664,414, 669,- 128, 670,552, 671,490,671,953, 672,035 and 672,036. The grinding, however, can also beperformed to such an extent that the result is only a suspension offibrils, which, according to German Pat. 875,389 and US. Pat. 2,039,-262, can be made into high-strength filaments and strings of collagen,which in turn can be used in surgery or in the manufacture of musicalinstrument strings.

Collagen can also be made by a freezing process into foams which are ofmedical interest, as explained in Journal of the American LeatherChemist Association (1964), pages 587 sqq.

Now, for many purposes it would be desirable to strengthen thesecollagen compositions by the incorporation of reinforcing fibers. It isknown that a fiber-reinforced sheet material has a substantially greaterstrength than the plain sheet. If, for example, it were desired tostrengthen cellulose sheets by the incorporation of fibers,

3,806,350 Patented Apr. 23, 1974 ice this would involve no particulardifficulty, because a thin ester solution of organic cellulose having alow viscosity can be prepared, into which cellulose fibers could then bedispersed according to German Pat. 568,820, for example.

The inorporation of fibers into a collagen mass, how ever, involvesconsiderable difiiculty because, in contrast to ester solutions ofcellulose, this mass is very viscous, i.e. dough-like. Artificial fiberscan, of course, 'be stirred into the collagen composition that isobtainable according to the patents cited above. However, they alwaysclump together, so that the distribution of the fibers within thecollagen composition is extremely irregular.

It is accordingly an object of the invention to provide a simpleprocedure for distributing a fibrous reinforcement substantiallyuniformly through collagen.

This and other objects and advantages are realized in accordance withthe present invention wherein a waterswollen collagen mass isde-swollen, i.e. dehydrated or shrunk, and a fiber reinforcement is thenadded. The collagen may thereafter be re-swollen and the fibers willremain distributed therethrough, although for some purposes suchre-swelling is not necessary.

A collagen mass prepared according to German Pat. 671,953 or any otherof the above-named patents contains only about 8 to 12% solid matter.The rest, i.e., about 88 to 92%, is water. Thus, the ratio of water tocollagen may range from about 92:8 to 88:12, i.e. about 12 to 7:1. Thewater is bound and distributed uniformly within the mass, chemically andphysically, so that the swollen, i.e., hydrated, mass is in a jelly-likestate of dough-like consistency. As stated above, it is impossible tostir short fibers, and therefore certainly not longer reinforcementslike staple fibers, uniformly into a jelly of this kind.

Now, according to the invention, a shrinking is first effected. This canbe accomplished simply by raising the pH of the collagen mass, which isabout 3, to about 5, whereupon there is formed an aqueous phase havingdispersed therein a network of shrunken, i.e., dehydrated or de-swollen,collagen fibers. It is then that the reinforcing fibers are stirred in,resulting in a uniform suspension of shrunken fibers and the addedfibers within the aqueous medium. This mass is then drained on a sieveuntil a mass is produced having a total solids weight of approximately25%. Then the pH is restored to about 3, resulting swelling, i.ehydration. The re-swollen hide fiber mass is then uniformly reinforcedwith the added fibers.

The added reinforcing fibers may be of substantially any type, e.g.nylon, polyester, polyolefin, acrylic or cellulosic, e.g. rayon, acetateor cotton, jute, sisal, hemp, and the like. Wool, glass fibers, metallicfibers, and the like may also be employed although they are lesspreferred for reasons of cost or properties. The reinforcing fiber mayrange in denier from as little as 1 or less to 50 or more, dependingupon the end use although normal textile deniers of from about 3 to 25are preferred for most purposes. Their length may be susbtantiallycontinuous, e.g. several meters or more in length, although preferablythey are of normal staple lengths and especially about 5 to 30 mm. Theamount of fiber added may range from about 0.1 to 10 times the weight ofthe waterfree collagen material. Outside these limits the product, hastoo much the character of only one of the components.

It has proven desirable for some purposes to include in the product anester of polyacrylic acid or a polyvinyl chloride, e.g. polyvinylchloride, polyvinylidene chloride, and the like. Advantageously, thesepolymers are added, in the form of dispersions or latices, to thecollagen-fiber composition before re-swelling (if undertaken) iscomplete; preferably before re-swelling is initiated. Alternatively,however, they can be added during the re-swelling or even beforede-swelling. The amount added may range from about 1 to 10% by weight ofthe fiber plus collagen, preferably approximately 2%. An especiallysuitable additive is the 40% dispersion of polyacrylic ester in watersold by BASF under the trademark Acronal, the material being stirredinto the de-swollen slurry of collagen in water.

The invention will be further described in the following illustrativeexamples wherein all parts are by weight unless otherwise stated.

EXAMPLE 1 A homogeneous water-swollen collagen mass at pH 3.0 and havinga solids content of 13%, is diluted to a solids content of 3%, and atthe same time the pH is increased to 5.0 by the addition of soda lye. Anaqueous suspension of collagen fibers is obtained. To 100 kg. of thissuspension 9 kg. of short nylon-6 fibers (10 mm., 1.3 d-tex) are addedin a sinusoidal mixer. After a mixing period of 1 minute, a uniformmixture of collagen fibers and nylon fibers is obtained. The fibrousmass is drained on a sieve until a total solids content of approximately25% is achieved. If the pH is then raised to 3.0 while stirring as theviscosity rises, a moldable composition is obtained which contains about6% collagen and 18% nylon fibers in substantially uniform distribution.

EXAMPLE 2 100 kg. of a swollen collagen mass (pH 3.0, 13% solids) ismixed in a kneader with 10 kg. of the collagennylon fiber mixtureobtained according to Example 1. A moldable composition is obtained,which contains about 13% of nylon fibers based on the weight ofcollagen.

EXAMPLE 3 The procedure is the same as in Example 1, but the 9 kg. ofnylon fibers are a mixture of three kilograms each of fibers mm., mm.and 15 mm. long.

EXAMPLE 4 Substantially similar results are achieved substituting forthe fibers of Example 3 fibers of 3.3 d-tex.

The products of the foregoing examples may be formed into shapedstructures such as films, e.g. sausage casings, by extrusion in the samemanner as unreinforced collagen and the water may be removed therefromas by drying and/or by coagulation of the extrudate by passing theextrudate through a bath of suitable pH or containing certain salts, asdescribed in British Pat. 429,040.

It is noteworthy that the production of fiber-reinforced collagen shapedstructures in accordance with the present invention can be performed onexisting collagen-handling equipment from the step of adding thereinforcing fibers to the extrusion and hardening, i.e. dewatering.

As noted hereinabove, the fibers may comprise nylon which has referenceto linear polyamides of any type including copolymers of one or moredicarboxylic acids such as adipic, sebacic, terephthalic or isophthalicacids and diamines such as hexamethylene diamine and the like,aminocarboxylic acids or their lactams such as caprolactam, and thelike, as well as interpolymers thereof. Polyester has reference tolinear polyesters of the same dicarboxylic acids noted hereinabove, forexample, with glycols such as one or more of ethylene glycol, butyleneglycol, ethylene diglycol, and the like. Polyolefins has referenceprincipally to polyethylene, polyropylene and polybutylene. Suitableacrylic fibers comprise copolymers of acrylonitrile with methylacrylate, ethyl acrylate, and the like. Other fibers may be similarlyemployed since they perform a physical rather than a chemical function.The fiber length may vary but it is preferably at least about 10' mm.for maximum reinforcing action.

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:

1. Process for the manufacture of a moldable collagen material havingstaple fibers uniformly distributed therethrough from an acidwater-swollen collagen mass, comprising de-swelling said mass byincreasing the pH to at least about 5 to form a liquid phase and ade-swollen collagen phase, stirring reinforcing staple fibers into saidliquid phase in the absence of a tanning agent, whereby such fibrousmaterial is uniformly distributed relative to said collagen material,and subsequently re-acidifying said mixture whereby the collagenre-swells to the original moldable state.

2. The process according to claim 1, wherein said fibrous materialcomprises at least one of nylon, polyester, polyolefin, acrylic, rayon,cellulose acetate or cotton.

3. The process according to claim 1, wherein said fibrous materialcomprises staple fibers ranging in length from about 5 to 30 mm.

4. The process according to claim 1, wherein said fibrous material isadded in an amount ranging from about 0.1 to 10 times the weight of theWater-free collagen material.

5. The process according to claim 1, including the further step ofadding to said mass an ester of polyacrylic acid or a polyvinyl chloridein an amount ranging from about 1 to 10% by weight of the water-freecollagen material plus fibrous material, said addition being efi'ectedprior to re-swelling.

6. The process according to claim 5, wherein said staple fibers are fromabout 5 to 30 mm. in length, comprise at least one of nylon, polyester,polyolefin, acrylic, rayon, acetate or cotton and are added in an amountranging from about 0.1 to 10 times the weight of the water-free collagenmaterial.

7. The process according to claim 6, including the further step offorming said fiber-reinforced collagen mass into a predetermined shape,and removing the water therefrom.

8. A sausage casing comprising collagen having distributed substantiallyuniformly therethrough about 0.1 to 10 times its weight of staple fibersand about 1 to 10% by weight of an ester of polyacrylic acid orpolyvinyl chloride by weight of the collagen plus fibrous material, saidstaple fibers being from about 5 to 30 mm. in length and comprising atleast one of nylon, polyester, polyolefin, acrylic, rayon, celluloseacetate or cotton.

References Cited UNITED STATES PATENTS 3,3 03,038 2/1967 Klevens 106-155THEORORE MORRIS, Primary Examiner US. Cl. X.R.

